Explicitly choose x86 softfloat/hardfloat ABI #136146

RalfJung · 2025-01-27T17:23:03Z

Part of #135408:
Instead of choosing this based on the target features listed in the target spec, make that choice explicit.
All built-in targets are being updated here; custom (JSON-defined) x86 (32bit and 64bit) softfloat targets need to explicitly set rustc-abi to x86-softfloat.

rustbot · 2025-01-27T17:23:11Z

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rustbot · 2025-01-27T17:23:13Z

These commits modify compiler targets.
(See the Target Tier Policy.)

RalfJung · 2025-01-27T17:30:51Z

Cc @workingjubilee

cjgillot · 2025-01-28T00:01:51Z

r? compiler

RalfJung · 2025-01-28T01:41:41Z

compiler/rustc_target/src/target_features.rs

-    ("soft-float", Stability::Forbidden { reason: "unsound because it changes float ABI" }, &[]),
+    // This cannot actually be toggled, the ABI always fixes it, so it'd make little sense to
+    // stabilize. It must be in this list for the ABI check to be able to use it.
+    ("soft-float", Stability::Unstable(sym::x87_target_feature), &[]),


Making this "forbidden" just leads to duplicate warnings so there's little point in doing that.

This makes riscv's forced-atomics the only remaining "forbidden" feature.

That makes sense to me.

workingjubilee

My understanding is that while it changes some error outputs, this PR shouldn't have any practical effect on people, correct? Except those using our unstable target-spec.json, I suppose, and they bought the ticket for the ride they're going to get.

r=me with nits addressed

workingjubilee · 2025-01-28T02:47:41Z

compiler/rustc_target/src/spec/json.rs

+                    match s.parse::<super::RustcAbi>() {
+                        Ok(rustc_abi) => base.$key_name = Some(rustc_abi),
+                        _ => return Some(Err(format!(
+                            "'{s}' is not a valid value for rust-abi. \


Suggested change

"'{s}' is not a valid value for rust-abi. \

"'{s}' is not a valid value for rustc-abi. \

workingjubilee · 2025-01-28T02:48:53Z

compiler/rustc_target/src/spec/mod.rs

+/// The Rustc-specific variant of the ABI used for this target.
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum RustcAbi {
+    /// On x86-32/64 only: do not use any FPU or SIMD registers for the ABI/


the "ABI/"?

RalfJung · 2025-01-28T02:59:38Z

My understanding is that while it changes some error outputs, this PR shouldn't have any practical effect on people, correct? Except those using our unstable target-spec.json, I suppose, and they bought the ticket for the ride they're going to get.

Correct, for custom target specs this can add -soft-float if you don't also set rustc-abi: "x86-softfloat". This is probably surprising as there is no warning about this, it just silently happens.

Maybe we should land #136147 first; that would avoid changing behavior for target-spec users and instead just emit a warning.

workingjubilee · 2025-01-28T03:02:20Z

I'm not worried about being maximally convenient for them, but either way. I'll try to review that when I finish my tea.

lcnr · 2025-01-28T10:33:13Z

r? @workingjubilee

rustbot · 2025-01-28T10:33:16Z

Could not assign reviewer from: workingjubilee.
User(s) workingjubilee are either the PR author, already assigned, or on vacation. Please use r? to specify someone else to assign.

bors · 2025-01-29T08:44:17Z

☔ The latest upstream changes (presumably #136225) made this pull request unmergeable. Please resolve the merge conflicts.

RalfJung · 2025-01-29T10:12:36Z

@bors r=workingjubilee

This additional field is required by the Rust compiler since rust-lang/rust#136146 .

The Rust compiler now requires an explicit `rustc-abi: x86-softfloat` field when using the soft-float target feature. This was added in rust-lang/rust#136146 and is part of the latest nightlies. I updated the post branches in commit 688a21e

commit 6273a05 upstream. When using Rust on the x86 architecture, we are currently using the unstable target.json feature to specify the compilation target. Rustc is going to change how softfloat is specified in the target.json file on x86, thus update generate_rust_target.rs to specify softfloat using the new option. Note that if you enable this parameter with a compiler that does not recognize it, then that triggers a warning but it does not break the build. [ For future reference, this solves the following error: RUSTC L rust/core.o error: Error loading target specification: target feature `soft-float` is incompatible with the ABI but gets enabled in target spec. Run `rustc --print target-list` for a list of built-in targets - Miguel ] Cc: <stable@vger.kernel.org> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs). Link: rust-lang/rust#136146 Signed-off-by: Alice Ryhl <aliceryhl@google.com> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # for x86 Link: https://lore.kernel.org/r/20250203-rustc-1-86-x86-softfloat-v1-1-220a72a5003e@google.com [ Added 6.13.y too to Cc: stable tag and added reasoning to avoid over-backporting. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Linux v6.14-rc3 contains commit 6273a058383e ("x86: rust: set rustc-abi=x86-softfloat on rustc>=1.86.0"), which resolves the error from rust-lang#136146. Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

CI: rfl: move job forward to Linux v6.14-rc3 Linux v6.14-rc3 contains commit 6273a058383e ("x86: rust: set rustc-abi=x86-softfloat on rustc>=1.86.0"), which resolves the error from rust-lang#136146. r? `@lqd` `@Kobzol` try-job: x86_64-rust-for-linux `@rustbot` label A-rust-for-linux `@bors` try

commit 6273a05 upstream. When using Rust on the x86 architecture, we are currently using the unstable target.json feature to specify the compilation target. Rustc is going to change how softfloat is specified in the target.json file on x86, thus update generate_rust_target.rs to specify softfloat using the new option. Note that if you enable this parameter with a compiler that does not recognize it, then that triggers a warning but it does not break the build. [ For future reference, this solves the following error: RUSTC L rust/core.o error: Error loading target specification: target feature `soft-float` is incompatible with the ABI but gets enabled in target spec. Run `rustc --print target-list` for a list of built-in targets - Miguel ] Cc: <stable@vger.kernel.org> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs). Link: rust-lang/rust#136146 Signed-off-by: Alice Ryhl <aliceryhl@google.com> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # for x86 Link: https://lore.kernel.org/r/20250203-rustc-1-86-x86-softfloat-v1-1-220a72a5003e@google.com [ Added 6.13.y too to Cc: stable tag and added reasoning to avoid over-backporting. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

CI: rfl: move job forward to Linux v6.14-rc3 Linux v6.14-rc3 contains commit 6273a058383e ("x86: rust: set rustc-abi=x86-softfloat on rustc>=1.86.0"), which resolves the error from rust-lang#136146. r? `@lqd` `@Kobzol` try-job: x86_64-rust-for-linux `@rustbot` label A-rust-for-linux `@bors` try

Rollup merge of rust-lang#137169 - ojeda:rfl, r=lqd CI: rfl: move job forward to Linux v6.14-rc3 Linux v6.14-rc3 contains commit 6273a058383e ("x86: rust: set rustc-abi=x86-softfloat on rustc>=1.86.0"), which resolves the error from rust-lang#136146. r? `@lqd` `@Kobzol` try-job: x86_64-rust-for-linux `@rustbot` label A-rust-for-linux `@bors` try

CI: rfl: move job forward to Linux v6.14-rc3 Linux v6.14-rc3 contains commit 6273a058383e ("x86: rust: set rustc-abi=x86-softfloat on rustc>=1.86.0"), which resolves the error from rust-lang/rust#136146. r? `@lqd` `@Kobzol` try-job: x86_64-rust-for-linux `@rustbot` label A-rust-for-linux `@bors` try

When using Rust on the x86 architecture, we are currently using the unstable target.json feature to specify the compilation target. Rustc is going to change how softfloat is specified in the target.json file on x86, thus update generate_rust_target.rs to specify softfloat using the new option. Note that if you enable this parameter with a compiler that does not recognize it, then that triggers a warning but it does not break the build. [ For future reference, this solves the following error: RUSTC L rust/core.o error: Error loading target specification: target feature `soft-float` is incompatible with the ABI but gets enabled in target spec. Run `rustc --print target-list` for a list of built-in targets - Miguel ] Cc: <stable@vger.kernel.org> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs). Link: rust-lang/rust#136146 Signed-off-by: Alice Ryhl <aliceryhl@google.com> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # for x86 Link: https://lore.kernel.org/r/20250203-rustc-1-86-x86-softfloat-v1-1-220a72a5003e@google.com [ Added 6.13.y too to Cc: stable tag and added reasoning to avoid over-backporting. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

commit 6273a05 upstream. When using Rust on the x86 architecture, we are currently using the unstable target.json feature to specify the compilation target. Rustc is going to change how softfloat is specified in the target.json file on x86, thus update generate_rust_target.rs to specify softfloat using the new option. Note that if you enable this parameter with a compiler that does not recognize it, then that triggers a warning but it does not break the build. [ For future reference, this solves the following error: RUSTC L rust/core.o error: Error loading target specification: target feature `soft-float` is incompatible with the ABI but gets enabled in target spec. Run `rustc --print target-list` for a list of built-in targets - Miguel ] Cc: <stable@vger.kernel.org> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs). Link: rust-lang/rust#136146 Signed-off-by: Alice Ryhl <aliceryhl@google.com> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # for x86 Link: https://lore.kernel.org/r/20250203-rustc-1-86-x86-softfloat-v1-1-220a72a5003e@google.com [ Added 6.13.y too to Cc: stable tag and added reasoning to avoid over-backporting. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> (cherry picked from commit 93893d74135780f2d98b25312603bc91ee31caac) Signed-off-by: Jack Vogel <jack.vogel@oracle.com>

softfloat must be declared more explicitely now. See: rust-lang/rust#136146 Signed-off-by: Markus Theil <theil.markus@gmail.com>

This is a direct port of the Tom Dohrmann's PR: rust-osdev/bootloader#492 Which, in turn, "fixes a nightly breakage introduced by": rust-lang/rust#136146

This is a direct port of the Tom Dohrmann's PR: rust-osdev/bootloader#492 Which, in turn, "fixes a nightly breakage introduced by": rust-lang/rust#136146 Signed-off-by: Panagiotis "Ivory" Vasilopoulos <git@n0toose.net>

When using Rust on the x86 architecture, we are currently using the unstable target.json feature to specify the compilation target. Rustc is going to change how softfloat is specified in the target.json file on x86, thus update generate_rust_target.rs to specify softfloat using the new option. Note that if you enable this parameter with a compiler that does not recognize it, then that triggers a warning but it does not break the build. [ For future reference, this solves the following error: RUSTC L rust/core.o error: Error loading target specification: target feature `soft-float` is incompatible with the ABI but gets enabled in target spec. Run `rustc --print target-list` for a list of built-in targets - Miguel ] Cc: <stable@vger.kernel.org> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs). Link: rust-lang/rust#136146 Signed-off-by: Alice Ryhl <aliceryhl@google.com> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> # for x86 Link: https://lore.kernel.org/r/20250203-rustc-1-86-x86-softfloat-v1-1-220a72a5003e@google.com [ Added 6.13.y too to Cc: stable tag and added reasoning to avoid over-backporting. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rustbot assigned cjgillot Jan 27, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 27, 2025

RalfJung force-pushed the x86-abi branch from 9a08be7 to 98dc988 Compare January 27, 2025 17:27

RalfJung mentioned this pull request Jan 27, 2025

x86: use SSE2 to pass float and SIMD types #135408

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RalfJung changed the title ~~Explicit choose x86 softfloat/hardfloat ABI~~ Explicitly choose x86 softfloat/hardfloat ABI Jan 27, 2025

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rustbot assigned lcnr and unassigned cjgillot Jan 28, 2025

workingjubilee assigned workingjubilee and unassigned lcnr Jan 28, 2025

RalfJung force-pushed the x86-abi branch 3 times, most recently from bd35e7c to 89fa12a Compare January 28, 2025 01:40

RalfJung commented Jan 28, 2025

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RalfJung force-pushed the x86-abi branch from 89fa12a to 438bd1b Compare January 28, 2025 02:51

workingjubilee approved these changes Jan 28, 2025

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RalfJung force-pushed the x86-abi branch from 438bd1b to 9f1a635 Compare January 28, 2025 02:58

RalfJung force-pushed the x86-abi branch from 9f1a635 to 11c35f3 Compare January 29, 2025 09:59

phil-opp added a commit to phil-opp/blog_os that referenced this pull request Feb 10, 2025

Set rustc-abi: x86-softfloat in target JSON

688a21e

This additional field is required by the Rust compiler since rust-lang/rust#136146 .

phil-opp mentioned this pull request Feb 10, 2025

Add rustc-abi field to target spec JSON phil-opp/blog_os#1393

Merged

ojeda mentioned this pull request Feb 17, 2025

CI: rfl: move job forward to Linux v6.14-rc3 #137169

Merged

egkoppel added a commit to popcorn-2/popcorn-2 that referenced this pull request Mar 24, 2025

Update target json for rust-lang/rust#136146

61b3d4b

thillux added a commit to thillux/nixpkgs that referenced this pull request May 14, 2025

rust-hypervisor-firmware: fix build with current rust

7a819ad

softfloat must be declared more explicitely now. See: rust-lang/rust#136146 Signed-off-by: Markus Theil <theil.markus@gmail.com>

n0toose mentioned this pull request Jun 4, 2025

change rustc-abi in custom targets to x86-softfloat rust-vmm/xen#15

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levinwinter mentioned this pull request Sep 1, 2025

ICE: assertion failed: layout.is_sized() #146084

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	"'{s}' is not a valid value for rust-abi. \
	"'{s}' is not a valid value for rustc-abi. \

Explicitly choose x86 softfloat/hardfloat ABI #136146

Explicitly choose x86 softfloat/hardfloat ABI #136146

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